反应详情

A solution of the benzophenone (17.5 g, 77.4 mmole) of Step A in ethylene bromide (26.5 mL) (containing a small amount of benzoyl peroxide) is heated at reflux. A solution of bromine (12.7 g, 79.6 mmole) in ethylene bromide (15 mL) is added dropwise over 30 minutes while the mixture is irradiated with a Photolamp (300 W). Reflux is continued for 17 hours (TLC, 9:1 petrolether-ethylacetate, traces of starting material still present). The solvent is removed in vacuo and the residue (brown oil, 39.22 g) is purified by flash chromatography (on silica Merck-60, preabsorbed in dichloromethane, eluted with 9:1 petrolether-ethyl acetate) to give unreacted starting material (2.59 g, ca. 15%) along with the desired product (14.36 g, 61% or 71.5% based on recovered unreacted starting material) and some mixed fraction (ca. 5.20 g). The light yellow solid melts at 58°-61° C. and it is used as such in the next step.

1. temperatureis heated
2. temperatureat reflux
3. customis irradiated with a Photolamp (300 W)
4. temperatureReflux
5. customThe solvent is removed in vacuo
6. customthe residue (brown oil, 39.22 g) is purified by flash chromatography (on silica Merck-60, preabsorbed in dichloromethane, eluted with 9:1 petrolether-ethyl acetate)